The isomerisation of allyl amines which may be prochiral using complexes of rhodium, iridium or ruthenium such as, for example, those represented by the formulae [Rh(P--P)*diene].sup.+ X.sup.-, [Rh(P--P)*.sub.2 ].sup.+ X.sup.-, [Ru(CH.sub.3 COO).sub.2 (P--P)*] or [RuY.sub.2 (P--P)*], in which (P--P)* is a bidentate phosphine ligand, "diene" stands for a diolefine such as cyclooctadiene or norbornadiene, X.sup.- is an anion such as a halide, BF.sup.-.sub.4, PF.sup.-.sub.6 or ClO.sup.-.sub.4, and Y is a halide, is known since several years. The isomerisation reaction gives the corresponding enamines or imines which are thereafter hydrolyzed to obtain chiral aldehydes, such as, for example, citronellal, methoxycitronellal or hydroxycitronellal. These latter are highly appreciated compounds in perfumery.
The above-mentioned processes are the object of several publications of which there are cited here the patents EP-B-068 506, 135 392 and 156 607 (patentee: Takasago Perfumery Co.) and JP 61-19203 of the same patentee, as well as the patent EP-B-398 132 (patentee: Hoffmann-La Roche AG) and the patent application EP 643 065 (applicant: Bayer AG). All the processes described in these references make use of catalysts which carry chiral bidentate phosphines which are derived from biphenyl or binapthyl system. The best known ligand for this isomerisation reaction (and which, moreover, also finds use in other catalytical application is the ligand known under the name of BINAP, which is represented by the following formula (IV) ##STR1##
We were not able to find in any prior art reference on the isomerisation of allylamines, in particular the stereospecific isomerisation, any example for the use of another ligand type as the one described above, namely a bidentate phosphine ligand derived from atropisomeric biaryles.
It may thus be surprising that we have succeeded to develop another catalytic system which uses chiral phosphorous ligands of a different type, derived from ferrocene, the chirality of which is not based on an atropic isomerism. In a further embodiment of the invention, there are used phosphine ligands which are derived from steroids. All these ligands have shown to be very useful for the above-mentioned isomerisation of prochiral allylamines.